Speed control method

ABSTRACT

A method for controlling an engine having both an electronically controlled inlet device, such as an electronic throttle unite, and an electronically controlled outlet device, such as a variable cam timing system is disclosed. The method of the present invention achieves cylinder air charge control that is faster than possible by using an inlet device alone. In other words, the method of the present invention controls cylinder air charge faster than manifold dynamics by coordination of the inlet and outlet device. This improved control is used to improve various engine control functions.

FIELD OF THE INVENTION

[0001] The field of the invention relates to engine speed control ininternal combustion engines.

BACKGROUND OF THE INVENTION

[0002] A vehicle's engine typically utilizes an idle speed control modewhere engine speed is controlled to a desired speed when a vehicle isstationary or slowly moving and an operator is not requesting drivetorque. During idle conditions, it is desirable to maintain a constantengine speed, thereby giving the operator superior drive feel. To keepengine speed constant, idle speed control should reject engine torquedisturbances from various sources, such as, for example, airconditioning systems, power steering systems, changes in ambientconditions, or changes in any other devices that affect engine speed.

[0003] One method for controlling engine speed to a desired speed usesignition timing, throttle position, or a combination of both. In onesystem a torque reserve is used so that it is possible to rapidlyincrease engine torque using ignition timing, thereby controlling enginespeed. One example of a system using ignition timing is disclosed inU.S. Pat. No. 5,765,527.

[0004] The inventors herein have recognized several disadvantages withthe above approaches. In particular, a disadvantage with using throttleposition is that the throttle cannot quickly change engine torque sinceit controls flow entering an intake manifold. Controlling flow enteringthe manifold cannot rapidly control cylinder charge due to manifoldvolume. For example, if the throttle is instantly closed, cylinder aircharge does not instantly decrease to zero. The engine must pump downthe air stored in the manifold, which takes a certain number ofrevolutions. Therefore, the cylinder air charge gradually decreasestoward zero.

[0005] Another disadvantage with the known approaches is related toignition timing. In particular, to maximize fuel economy, ignitiontiming should be at MBT timing (ignition timing for maximum torque).However, when at MBT, adjustment of ignition timing in any directiondecreases engine torque and fuel economy. Therefore, when maximizingfuel economy, load torques cannot be rejected since ignition timing canonly decrease engine torque. To be able to use ignition timing in bothpositive and negative directions, ignition timing must be set away fromMBT timing. This allows rapid engine torque control, but at the cost ofdegraded fuel economy.

SUMMARY OF THE INVENTION

[0006] An object of the present invention is to rapidly control enginespeed to a desired engine speed while maximizing fuel economy.

[0007] The above object is achieved and disadvantages of priorapproaches overcome by a method for controlling speed of an enginehaving at least one cylinder, the engine also having an intake manifoldand an outlet control device for controlling flow from the intakemanifold into the cylinder, comprising: generating a desired enginespeed; and changing the outlet control device to control the enginespeed to said desired engine speed.

[0008] By using an outlet control device that controls flow exiting themanifold (entering the cylinder), it is possible to rapidly changeengine torque and engine speed, despite response delays of airflowinducted through the intake manifold. In other words, a rapid change incylinder charge can be achieved, thereby allowing a rapid change incylinder air/fuel ratio while preventing disturbances in engine torque.

[0009] An advantage of the above aspect of the invention is that enginespeed can be more accurately controlled to a desired engine speedwithout fuel economy degradation.

[0010] In another aspect of the present invention, the above object isachieved and disadvantages of prior approaches overcome by a method forcontrolling speed of an engine having at least one cylinder, the enginealso having an intake manifold and an outlet control device forcontrolling flow from the intake manifold into the cylinder and an inletcontrol device for controlling flow into the intake manifold,comprising: generating a desired engine speed; and changing both theoutlet control device and the inlet control device based on the enginespeed and said desired engine speed and in response to a respectiveoutlet control device command and an inlet control device command.

[0011] By changing both the inlet and outlet control devices, it ispossible to rapidly change engine torque and engine speed despiteresponse delays of airflow inducted through the intake manifold. Sincethe cylinder air charge can be rapidly changed, the cylinder air/fuelratio change can be compensated and abrupt changes in engine torque canbe avoided. In other words, the present invention controls manifoldinlet and outlet flows in a coordinated way to allow a rapid change inengine speed regardless of manifold volume. This rapid cylinder aircharge change allows torque disturbances to by rapidly rejected withoutusing an ignition timing torque reserve.

[0012] An advantage of the above aspect of the invention is thatsustained torque disturbances can rejected.

[0013] Another advantage of the above aspect of the invention is that byusing both an outlet and an inlet control device, a more controlledrapid change in engine torque and engine speed.

[0014] Other objects, features and advantages of the present inventionwill be readily appreciated by the reader of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The object and advantages of the invention claimed herein will bemore readily understood by reading an example of an embodiment in whichthe invention is used to advantage with reference to the followingdrawings wherein:

[0016]FIGS. 1A and 1B are a block diagrams of an embodiment in which theinvention is used to advantage;

[0017]FIG. 2A is a block diagram of an embodiment in which the inventionis used to advantage;

[0018]FIGS. 2B-20 are graphs describing operation of the embodiment inFIG. 2A;

[0019]FIGS. 3-5, 8-10 are high level flowcharts which perform a portionof operation of the embodiment shown in FIGS. 1A, 1B, and 2A;

[0020]FIG. 6 is a graph showing how various factors are related toengine operation according to the present invention;

[0021]FIG. 7 is a graph depicting results using the present invention;

[0022]FIGS. 11A-11F are graphs describing operation of an embodiment ofthe present invention; and

[0023]FIGS. 12 and 14 are a block diagrams of an embodiment in which theinvention is used to advantage.

DESCRIPTION OF PREFERRED EMBODIMENT(S)

[0024] Direct injection spark ignited internal combustion engine 10,comprising a plurality of combustion chambers, is controlled byelectronic engine controller 12. Combustion chamber 30 of engine 10 isshown in FIG. 1A including combustion chamber walls 32 with piston 36positioned therein and connected to crankshaft 40. In this particularexample piston 30 includes a recess or bowl (not shown) to help informing stratified charges of air and fuel. Combustion chamber, orcylinder, 30 is shown communicating with intake manifold 44 and exhaustmanifold 48 via respective intake valves 52 a and 52 b (not shown), andexhaust valves 54 a and 54 b (not shown). Fuel injector 66A is showndirectly coupled to combustion chamber 30 for delivering liquid fueldirectly therein in proportion to the pulse width of signal fpw receivedfrom controller 12 via conventional electronic driver 68. Fuel isdelivered to fuel injector 66A by a conventional high pressure fuelsystem (not shown) including a fuel tank, fuel pumps, and a fuel rail.

[0025] Intake manifold 44 is shown communicating with throttle body 58via throttle plate 62. In this particular example, throttle plate 62 iscoupled to electric motor 94 so that the position of throttle plate 62is controlled by controller 12 via electric motor 94. This configurationis commonly referred to as electronic throttle control (ETC) which isalso utilized during idle speed control. In an alternative embodiment(not shown), which is well known to those skilled in the art, a bypassair passageway is arranged in parallel with throttle plate 62 to controlinducted airflow during idle speed control via a throttle control valvepositioned within the air passageway.

[0026] Exhaust gas oxygen sensor 76 is shown coupled to exhaust manifold48 upstream of catalytic converter 70. In this particular example,sensor 76 provides signal EGO to controller 12 which converts signal EGOinto two-state signal EGOS. A high voltage state of signal EGOSindicates exhaust gases are rich of stoichiometry and a low voltagestate of signal EGOS indicates exhaust gases are lean of stoichiometry.Signal EGOS is used to advantage during feedback air/fuel control in aconventional manner to maintain average air/fuel at stoichiometry duringthe stoichiometric homogeneous mode of operation.

[0027] Conventional distributorless ignition system 88 provides ignitionspark to combustion chamber 30 via spark plug 92 in response to sparkadvance signal SA from controller 12.

[0028] Controller 12 causes combustion chamber 30 to operate in either ahomogeneous air/fuel mode or a stratified air/fuel mode by controllinginjection timing. In the stratified mode, controller 12 activates fuelinjector 66A during the engine compression stroke se that fuel issprayed directly into the bowl of piston 36. Stratified air/fuel layersare thereby formed. The strata closest to the spark plug contains astoichiometric mixture or a mixture slightly rich of stoichiometry, andsubsequent strata contain progressively leaner mixtures. During thehomogeneous mode, controller 12 activates fuel injector 66A during theintake stroke so that a substantially homogeneous air/fuel mixture isformed when ignition power is supplied to spark plug 92 by ignitionsystem 88. Controller 12 controls the amount of fuel delivered by fuelinjector 66A so that the homogeneous air/fuel mixture in chamber 30 canbe selected to be at stoichiometry, a value rich of stoichiometry, or avalue lean of stoichiometry. The stratified air/fuel mixture will alwaysbe at a value lean of stoichiometry, the exact air/fuel being a functionof the amount of fuel delivered to combustion chamber 30. An additionalsplit mode of operation wherein additional fuel is injected during theexhaust stroke while operating in the stratified mode is also possible.

[0029] Nitrogen oxide (NOx) absorbent or trap 72 is shown positioneddownstream of catalytic converter 70. NOx trap 72 absorbs NOx whenengine 10 is operating lean of stoichiometry. The absorbed NOx issubsequently reacted with HC and catalyzed during a NOx purge cycle whencontroller 12 causes engine 10 to operate in either a rich homogeneousmode or a stoichiometric homogeneous mode.

[0030] Controller 12 is shown in FIG. 1A as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 104, anelectronic storage medium for executable programs and calibration valuesshown as read only memory chip 106 in this particular example, randomaccess memory 108, keep alive memory 110, and a conventional data bus.Controller 12 is shown receiving various signals from sensors coupled toengine 10, in addition to those signals previously discussed, including:measurement of inducted mass air flow (MAP) from mass air flow sensor100 coupled to throttle body 58; engine coolant temperature (ECT) fromtemperature sensor 112 coupled to cooling sleeve 114; a profile ignitionpickup signal (PIP) from Hall effect sensor 118 coupled to crankshaft40; and throttle position TP from throttle position sensor 120; andabsolute Manifold Pressure Signal MAP from sensor 122. Engine speedsignal RPM is generated by controller 12 from signal PIP in aconventional manner and manifold pressure signal MAP provides anindication of engine load. In a preferred aspect of the presentinvention, sensor 118, which is also used as an engine speed sensor,produces a predetermined number of equally spaced pulses everyrevolution of the crankshaft.

[0031] In this particular example, temperature Tcat of catalyticconverter 70 and temperature Ttrp of NOx trap 72 are inferred fromengine operation as disclosed in U.S. Pat. No. 5,414,994 thespecification of which is incorporated herein by reference. In analternate embodiment, temperature Tcat is provided by temperature sensor124 and temperature Ttrp is provided by temperature sensor 126.

[0032] Continuing with FIG. 1A, camshaft 130 of engine 10 is showncommunicating with rocker arms 132 and 134 for actuating intake valves52 a, 52 b and exhaust valve 54 a. 54 b. Camshaft 130 is directlycoupled to housing 136. Housing 136 forms a toothed wheel having aplurality of teeth 138. Housing 136 is hydraulically coupled to an innershaft (not shown), which is in turn directly linked to camshaft 130 viaa timing chain (not shown). Therefore, housing 136 and camshaft 130rotate at a speed substantially equivalent to the inner camshaft. Theinner camshaft rotates at a constant speed ratio to crankshaft 40.However, by manipulation of the hydraulic coupling as will be describedlater herein, the relative position of camshaft 130 to crankshaft 40 canbe varied by hydraulic pressures in advance chamber 142 and retardchamber 144. By allowing high pressure hydraulic fluid to enter advancechamber 142, the relative relationship between camshaft 130 andcrankshaft 40 is advanced. Thus, intake valves 52 a, 52 b and exhaustvalves 54 a, 54 b open and close at a time earlier than normal relativeto crankshaft 40. Similarly, by allowing high pressure hydraulic fluidto enter retard chamber 144, the relative relationship between camshaft130 and crankshaft 40 is retarded. Thus, intake valves 52 a, 52 b andexhaust valves 54 a, 54 b open and close at a time later than normalrelative to crankshaft 40.

[0033] Teeth 138, being coupled to housing 136 and camshaft 130, allowfor measurement of relative cam position via cam timing sensor 150providing signal VCT to controller 12. Teeth 1, 2, 3, and 4 arepreferably used for measurement of cam timing and are equally spaced(for example, in a V-8 dual bank engine, spaced 90 degrees apart fromone another), while tooth 5 is preferably used for cylinderidentification, as described later herein. In addition, Controller 12sends control signals (LACT, RACT) to conventional solenoid valves (notshown) to control the flow of hydraulic fluid either into advancechamber 142, retard chamber 144, or neither.

[0034] Relative cam timing is measured using the method described inU.S. Pat. No. 5,548,995, which is incorporated herein by reference. Ingeneral terms, the time, or rotation angle between the rising edge ofthe PIP signal and receiving a signal from one of the plurality of teeth138 on housing 136 gives a measure of the relative cam timing. For theparticular example of a V-8 engine, with two cylinder banks and a fivetoothed wheel, a measure of cam timing for a particular bank is receivedfour times per revolution, with the extra signal used for cylinderidentification.

[0035] Referring now to FIG. 1B, a port fuel injection configuration isshown where fuel injector 66B is coupled to intake manifold 44, ratherthan directly cylinder 30.

[0036] Referring now to FIG. 2A, a more general diagram shows manifold44 a, with inlet flow, m_in, and outlet flow, m_out. Inlet flow, m_in,is governed by inlet control device 170. Outlet flow, m_out, is governedby outlet flow device 171. In a preferred embodiment, manifold 44 a isan intake manifold of an engine, inlet control device 170 is a throttle,and outlet control device 171 is a variable cam timing mechanism.However, as one skilled in the art would recognize, there are manyalternative embodiments of the present invention. For example, outletcontrol device could be a swirl control valve, a variable valve timingmechanism, a variable valve lift mechanism, or an electronicallycontrolled intake valve used in camless engine technology.

[0037] Continuing with FIG. 2A, there are other variables that affectflow entering and exiting manifold 44 a. For example, pressures p1 andp2, along with inlet control device 170, determine flow m_in. Similarly,pressures p2 and p3, along with outlet device 171 determine flow m_out.Therefore, flow storage in manifold 44 a, which dictates how fastpressure p2 can change, affects flow m_out. In an example where manifold44 a is an intake manifold of an engine operating at stoichiometry, flowm_out represents flow entering a cylinder and is directly proportionalto engine torque.

[0038]FIGS. 2B-2K illustrate the effect of such interrelationships onsystem performance. In FIG. 2B, inlet control device 170 is rapidlychanged at time t1. The resulting change in outlet flow (m_out) is shownin FIG. 2C. The resulting change in inlet flow (m_in) is shown in FIG.2D. This example has outlet control device 171 fixed, and thereforerepresents conventional engine operation and prior art operation wherethrottle position is used to control outlet flow (m_out). In thisexample, a rapid change in inlet control device 170 does not produce anequally rapid change in exit flow m_out.

[0039] According to the present invention, in FIG. 2E, outlet controldevice 171 is rapidly changed at time t2. The resulting change in outletflow (m_out) is shown in FIG. 2F. The resulting change in inlet flow(m_in) is shown in FIG. 2G. This example has inlet control device 170fixed, and therefore represents adjustment of outlet device 170 only tocontrol outlet flow (m_out). In this example, a rapid change in outletcontrol device 170 does produce an equally rapid change in exit flowm_out. However, the rapid change is not completely sustained.

[0040] According to the present invention, in FIG. 2H, inlet controldevice 170 is rapidly changed at time t3. Similarly, in FIG. 2I, outletcontrol device 171 is rapidly changed at time t3. The resulting changein outlet flow (m_out) is shown in FIG. 2J. The resulting change ininlet flow (m_in) is shown in FIG. 2K. This example varies both inletcontrol device 170 and outlet control device 170 concurrently. In thisexample, a rapid change in both inlet control device and 170 outletcontrol device 171 does produce an equally rapid change in exit flowm_out, where the rapid change is sustained.

[0041] According to the present invention, in FIG. 2L, inlet controldevice 170 is rapidly changed at time t4. Similarly, in FIG. 2M, outletcontrol device 171 is rapidly changed at time t4 to a greater extentthan in FIG. 2I. The resulting change in outlet flow (m_out) is shown inFIG. 2N. The resulting change in inlet flow (m_in) is shown in FIG. 20.This example varies both inlet control device 170 and outlet controldevice 170 concurrently. In this example, a rapid change in both inletcontrol device and 170 outlet control device 171 does produce an equallyrapid change in exit flow m_out, where the rapid change is sustained andactually produces a certain amount of peak, or overshoot. Thisrepresents how the present invention can be used to not only rapidlyproduce an increase in outlet flow, but to also add an overshoot. Thus,a control system according to the present invention can thereforegenerate a airflow lead control. Such lead control is advantageous forengine idle speed control to counteract engine inertia, or for vehiclelaunch conditions, to give improved drive feel.

[0042] According to the present invention, by using an outlet controldevice it is possible to rapidly control flow exiting a manifold.Further, by controlling both an inlet and outlet control device it ispossible to more accurately rapidly control flow exiting a manifold invarious shapes.

[0043] In cases where engine 10 operates at a stoichiometric air/fuelratio, then engine torque directly proportional to cylinder charge,which is in turn proportional to exit flow m_out and engine speed. Thus,according to the present invention, by controlling engine airflow to adesired value.

[0044] Engine Idle Speed Control

[0045] Referring now to FIG. 3, a routine is described for controllingengine speed using both throttle position and cam timing. In step 310,an engine speed error (Nerr) is calculated based on a difference betweenthe desired engine speed (Ndes) and an actual engine speed (Nact). Then,in step 320, the desired change in cylinder charge is calculated fromspeed error using controller K1, where controller K1 is represented inthe Laplace domain as K1(s) as is known to those skilled in the art. Thedesired in cylinder charge (Amcyl) is preferably calculated using aproportional controller. Therefore, in the preferred embodiment,controller K1 represents a proportional controller. However, as thoseskilled in the art will recognize, various other control schemes can beused in place of proportional controller K1. For example, proportionalintegral derivative controllers, or sliding mode controllers, or anyother controllers known to those skilled in the art, can be used. Next,in step 330, an intermediate throttle position (Tpint) is calculatedfrom speed error and controller K3. As described above, variouscontrollers can be used for controller K3. In a preferred embodiment,controller K3 is an integral controller. Next, in step 340, a nominalcam timing error (VCTerr) is calculated based on a difference between adesired nominal cam timing (VCTdesnom) and an actual cam timing(VCTact). Desired nominal cam timing (VCTdesnom) can be determined basedon operating conditions, for example, based on idle mode, or drive mode.Also, desired nominal cam timing (VCTdesnom) can be set as a function ofdesired engine torque, or any other steady state scheduling method knownto those skilled in the art. Next, in step 350, an intermediate timing(VCTint) is calculated from nominal cam timing error and controller K2.Controller K2 can be any controller known to those skilled in the art.In the preferred embodiment, controller K2 is a proportional integralcontroller.

[0046] Referring now to FIG. 4, a routine is described for calculatingadjustments to cam timing and throttle position to rapidly changecylinder charge. First, in step 410, manifold pressure (Pm) is estimatedor measured using sensor 122. In the preferred embodiment, manifoldpressure (Pm) is estimated using methods known to those skilled in theart. For example, manifold pressure can be estimated using signal MAFfrom mass airflow sensor 100, engine speed, and other signals known tothose skilled in the art to effect manifold pressure. Next, in step 412,the desired change in cylinder charge (Ancyl) is read from FIG. 3. Next,in step 414, a change in cam timing (AVCT) is determined to give thedesired change in cylinder charge at manifold pressure (Pm) read in step410. Step 414 is performed using maps relating to cam timing, cylindercharge, and manifold pressure. The maps can be determined theoreticallyusing engine models or measured using engine test data. Next, in step416, a change in throttle position (ATP) is determined to give thedesired change in cylinder charge (Ancyl) at manifold pressure (Pm)determined in step 410. Step 416 is similarly performed usingcharacteristic maps relating parameters, throttle position, cylindercharge, and manifold pressure. The maps can be determined either usingengine models or engine test data.

[0047] Regarding FIG. 5, the routine is described for calculating thedesired cam timing and desired throttle position. First, in step 510, adesired cylinder, desired cam timing (VCTdes) is determined based on thedesired change in cam timing and intermediate cam timing. Next, in step512, the desired throttle position (TPdes) is determined based onintermediate throttle position and desired change in throttle position.

[0048] However, when a cam timing position is desired that is greaterthan a maximum possible cam timing, or when a minimum cam timing is lessthan a minimum possible cam timing, desired cam timing (VCTdes) isclipped to the maximum or minimum value. In other words adjustment ofcam timing may not be able to provide the desired increase, or decreasein cylinder air charge. In this case, cam timing is clipped to theachievable limit value and throttle position is relied upon to providecontrol.

[0049] Steady State Constraints

[0050] As described above herein with particular reference to FIGS. 3-5,a control method for controlling engine airflow, or engine torque, andthereby engine speed was described. In addition, the method included amethod for rapidly controlling cylinder charge using both an inlet andoutlet control device, while also relatively slowly controlling theoutlet control device to a nominal position. Both of these process arenow further illustrated using both FIGS. 6 and 7.

[0051] Referring now to FIG. 6, a graph is shown with throttle position(TP) on the vertical axis and cam timing (VCT) on the horizontal axis.Dash dotted lines are shown for constant values of engine torque (Te),assuming stoichiometric conditions, while solid lines show constantvalue of manifold pressure. According to the present invention, theengine can quickly change operating points along the lines of constantpressure

[0052] (thereby rapidly changing engine airflow and torque)

[0053] since there are no manifold dynamics in this direction. However,the engine can change only relatively slowly along the dash dotted linesif air/fuel ratio is fixed (for example at stoichiometry). The dashedvertical line represents the nominal desired cam timing for the givenoperating conditions. For example, the nominal timing for idleconditions, or the nominal timing for the current desired engine torque.

[0054] In other words, manifold dynamics represent dynamics associatedwith changing manifold pressure and explain why flow entering thecylinder is not always equal to flow entering the manifold. Manifoldpressure cannot instantly change due to manifold volume. As manifoldvolume increases, manifold dynamics become slower. Conversely, asmanifold volume decreases, manifold dynamics become faster. Thus,manifold dynamics, or manifold delay, is a function of manifold volume.As described above, when moving along lines of constant pressure,manifold dynamics are essentially immaterial. Therefore, flow changesare not limited by manifold dynamics when inlet and outlet controldevices are changed to affect flow in similar directions. By changinginlet and outlet control devices faster than manifold dynamics toincrease along both the abscissa and ordinate of FIG. 6, cylinder flowchanges faster than manifold dynamics. Stated another way, cylinder flowchanges faster than it would if only the inlet control device changedinfinitely fast. When inlet and outlet control devices are changed toaffect flow in opposite directions, cylinder charge can be keptconstant. In particular, both the inlet and outlet control devices arechanged slower than manifold dynamics since manifold pressure ischanged. This is particular useful when engine airflow, or enginetorque, is to be kept relatively constant yet it is desired to placeeither the inlet control device or the outlet control device in aspecified location.

[0055] Referring now to both FIGS. 6 and 7, an example of operationaccording to an aspect of the present invention is now described. First,the system is operating at point 1. For example, the desired enginetorque (Ted) is Te2, or this happens to be the engine torque to maintaina desired engine speed. Then, either the desired engine torque (Ted)changes to Te3, or a torque disturbance causes an engine speed to drop,thereby requiring an increase in engine torque to Te3 to maintain thedesired engine speed. At this point (time t5), controller 12 causes boththe throttle position and cam timing to change so that the engine systemquickly moves to point 2. Next, in order to maintain cam timing and thenominal cam timing, controller 12 causes both the throttle position andcam timing to move to point 3 at a rate slower than the manifolddynamics.

[0056] Thus, according to the present invention, throttle position andcam timing are caused to move in the following way. When it is desiredto rapidly increase cylinder air charge irrespective of manifoldvolume: 1) throttle position moves in a way that causes an increase inthrottle opening area, and 2) cam timing is adjusted in a way toincrease the inducted cylinder air charge for a given manifold pressuremoved. Similarly, when it is desired to rapidly decrease cylinder aircharge irrespective of manifold volume: 1) throttle position moves in away that causes a decrease in throttle opening area, and 2) cam timingis adjusted in a way to decrease the inducted cylinder air charge for agiven manifold pressure. Thus, it is possible to rapidly change andmaintain flow into the cylinder by this combined action.

[0057] However, when it is desired to maintain cylinder air charge andeither increase throttle opening or cause cam timing to move so thatless air charge is inducted for a given manifold pressure, or both, 1)throttle position moves in a way that causes an increase in throttleopening area, and 2) cam timing is adjusted in a way to decrease theinducted cylinder air charge for a given manifold pressure. Thus,cylinder charge can be kept constant by this opposing action.Alternatively, when it is desired to maintain cylinder air charge andeither decrease throttle opening or cause cam timing to move so thatmore air charge is inducted for a given manifold pressure, or both, 1)throttle position moves in a way that causes a decrease in throttleopening area, and 2) cam timing is adjusted in a way to increase theinducted cylinder air charge for a given manifold pressure. Again,cylinder charge can be kept constant by this opposing action.

[0058] Such coordinated control is advantageous in that steady stateoptimization constraints on cam timing can be provided while stillproviding the ability to control cylinder air charge rapidly.

[0059] Engine Torque Control

[0060] Referring now to FIG. 8, a routine is described for controllingengine torque rather than engine speed as described in FIG. 3. Enginetorque control according to the present invention may be used forvarious reasons, including normal driving operating, traction control,and/or cruise control. In other words, FIG. 8, along with FIGS. 3-5 canbe used to control engine torque, where steps 310-330 are replaced byFIG. 8. Regarding FIG. 8, first, in step 810, a desired engine torque(Ted) is determined. Those skilled in the art will recognize thatdesired engine torque (Ted) can be determined in various ways. Forexample, desired engine torque (Ted) can be determine from desired wheeltorque and gear ratio, from pedal position and vehicle speed, from pedalposition and engine speed, or any other method known to those skilled inthe art. Then, in step 820, desired cylinder charge (mcyld) isdetermined based on a function (h) of desired engine torque (Ted).Function (h) is based on a desired air/fuel ratio, such asstoichiometric conditions.

[0061] Continuing with FIG. 8, in step 830, desired change in cylindercharge (Dmcyl) is determined based on the difference between desiredcylinder charge (mcyld) and actual cylinder charge (mcyl). Then, in step840, intermediate throttle position (Tpoint) is calculated from desiredchange in cylinder charge (Dmcyl) and controller K3. As described above,various controllers can be used for controller K3. In a preferredembodiment, controller K3 is an integral controller. Then, in step 850,a nominal cam timing (VCTdesnom) if determined based on function (g) anddesired engine torque (Ted). Then, the routine continues to step 340 inFIG. 3.

[0062] Alternative Embodiment for Cylinder Charge, Torque, and EngineSpeed Control

[0063] An alternative embodiment is now described that can be used tocontrol either cylinder air charge, Engine Torque at a given air/fuelratio, or engine speed. Referring now to FIG. 9, in step 910, adetermination is made as to whether the engine is currently in an idlecondition. Those skilled in the art will recognize various methods fordetermining idle conditions such as accelerator pedal position, enginespeed, and various other factors. When the answer to step 910 is YES,the routine continues to step 912. In step 912, the desired cylindercharge (mcyldes) based on an engine speed error (Nerr). The desiredcylinder charge is calculated using function L1, which can represent anyfunction such as, for example, engine speed error multiplied by aconstant gain, which is the preferred embodiment. Otherwise, when theanswer to step 910 is NO, the routine continues to step 914. In step914, the desired cylinder charge is calculated based on either a drivercommand or operating conditions using function (L2). Those skilled inthe art will recognize various methods for calculating a desiredcylinder charge from a driver command such as, for example, to provide adesired engine torque, a desired wheel torque, an engine output, orprovide any other condition requested by the driver. Those skilled inthe art will also recognize various operating conditions that can affecta desired cylinder charge such as, for example, engine startingconditions, cold conditions, or cranking conditions.

[0064] Continuing with FIG. 9, the routine continues from either step912 or step 914 to step 916. In step 916, a cylinder charge error(mcylerr) is calculated based on desired cylinder charge and actualcylinder charge (mcylact). Next, in step 918, cam timing nominal erroris calculated. Next, in step 920, intermediate cam timing is calculatedfrom cam timing nominal error and controller H1. In a preferredembodiment, controller H1 is an integral controller known to thoseskilled in the art. Also, in a preferred embodiment, the gains ofcontroller H1 are determined so that the cam timing is adjusted slowerthan manifold dynamics. In other words, the gains of controller H1 aredetermined based on manifold volume, and engine speed. However,controller H1 can be any controller known to those skilled in the artsuch as, for example, a PID controller, a PI controller, or a Pcontroller. Next, in step 930, intermediate throttle position iscalculated from cylinder charge error and controller H2. In a preferredembodiment, controller H2 is an integral controller; however, as thoseskilled in the art will recognize, various controllers can be used.Next, in step 940, a difference in cam timing is calculated fromcylinder charge error and controller H3. In a preferred embodiment,controller H3 is a lead controller or a high pass filter typecontroller. Next, the routine continues to step 950, where a differencein throttle position is calculated from the difference in cam timingusing controller H4. In a preferred embodiment, controller H4 is simplya constant gain. Next, the routine continues to FIG. 5.

[0065] Air/Fuel Constraints in Lean Conditions

[0066] Referring now to FIG. 10, a routine for restricting air/fuelratio to specific regions is described. In step 1010, a determination ismade as to whether the engine is operating in stratified conditions.When the answer to step 1010 is YES, the routine continues to step 1012.In step 1012, the required fuel injection amount (fi) is calculatedbased on driver commands or operating conditions. Again, those skilledin the art will recognize various methods for determining a fuelinjection amount based on driver command or engine operating conditions.Next, the routine continues to step 1014, where a restricted air rangeis calculated. The restricted air range is calculated using a maximumand minimum allowable air/fuel ratio, the fuel injection amount, and aband parameter (B). The band parameter is used to allow room forcalculation inaccuracies. Next, the routine continues to step 1016,where a determination is made as to whether actual cylinder charge isbetween the maximum and minimum allowable cylinder charges (mcyl1,mcyl2). When the answer to step 1016 is YES, a determination is thenmade in step 1018 as to whether it is possible, given the currentoperating conditions, to produce air charge (mcyl1). This determinationcan be made based on factors such as, for example, engine speed andatmospheric pressure. In particular, as atmospheric pressure increases,engine 10 is able to pump a greater maximum air amount. Therefore, in apreferred embodiment, limit mcyl1 is selected when atmospheric pressureis greater than a calibrated value, and mcyl2 is selected otherwise. Inother words, in step 1018, a determination is made as to whether theengine can physically produce upper air charge (mcyl1). When the answerto step 1018 is NO, the routine sets the desired cylinder charge(mcyldes) equal to lower air charge (mcyl2) in step 1020. Otherwise, thedesired cylinder charge is set to upper cylinder charge (mcyl1).

[0067] Referring now to FIG. 11, the present invention is compared toprior art approaches in controlling engine torque or keeping an air/fuelratio outside of a restricted air/fuel ratio range. The FIGS. 11athrough 11 f show a comparison of the present invention as representedby solid lines, and prior approaches as represented by dashed lines. Inprior approaches, as shown in FIG. 11a, fuel injection amount increasesat time T6 in response to a change in desired engine torque shown inFIG. 11d. To maintain the air/fuel ratio at a desired point, as shown inFIG. 1e, increased airflow is required. To provide increased airflow,prior approaches change throttle position, as shown in FIG. 11c, at timeT6. However, because of airflow dynamics due to the manifold volume, aircharge does not increase fast enough, as shown in FIG. 11f. This resultsin a temporary excursion in the air/fuel ratio into the restrictedregion as shown in FIG. 11e. Thus, the prior approaches cannot keep theair/fuel ratio completely out of the restricted region.

[0068] According to the present invention, and as described in FIG. 10,at time T6, cam timing, as shown in FIG. 11b, is also increased. Thisallows the air/fuel ratio, as shown in FIG. 11e, to refrain fromentering the restricted air/fuel range. This is possible since theairflow was quickly changed using both cam timing and throttle positionas shown in FIG. 11f by the solid line.

[0069] Vehicle Launch Improvement

[0070] Vehicle driveability is improved according to the presentinvention by providing engine torque increases at a rate faster thanavailable by prior art methods. Regarding FIG. 12, engine 10 is coupledto automatic transmission (AT) 1200 via torque converter (TC) 1210.Automatic transmission (AT) 1200 is shown coupled to drive shaft 1202,which in turn is coupled to final drive unit (FD) 1204. Final drive unit(FD) is coupled wheel 1208 via second drive shaft 1208. In thisconfiguration, engine 10 can be somewhat downsized and still produceacceptable drive feel by controlling engine torque or airflow using boththrottle position and cam timing as describe above herein.

[0071] Regarding FIG. 13, torque converter 1210 is removed. Thus, evenwithout downsizing engine 10, using prior approaches driveability isreduced. In other words, vehicle launch is normally assisting fromtorque multiplication provided by torque converter 1210. Without torqueconverter 1210, vehicle launch feel is degraded. To compensate for thelack of torque converter 1210, engine 10 is controlled according to thepresent invention using both throttle position and cam timing to rapidlyincrease engine torque or airflow, thereby improving drive feel andallowing elimination of torque converter 1210.

[0072] In a preferred embodiment, during vehicle launch at low vehiclespeed and low engine speed, both inlet control device and outlet controldevice 170 and 171 are coordinated to rapidly control engine cylindercharge, thereby improving drive feel. Further to enable such operating,nominal cam timing (VCTdesnom) is set to a value where a large potentialincrease in cylinder air charge can be achieved when the transmission isin drive and vehicle speed is below a predetermine vehicle speedindicating potential for vehicle launch.

[0073] Turbo Lag Compensation

[0074] Referring now to FIG. 14, a configuration is shown where engine10 is coupled to a compression device 1400. In a preferred embodiment,compression device 1400 is a turbocharger. However, compression device1400 can be any compression device such as, for example, a supercharger.Engine 10 is shown coupled to intake manifold 44 b and exhaust manifold48 b. Also shown is outlet control device 171 coupled between intakemanifold 44 b and engine 10. Inlet control device 170 is also showncoupled between intake manifold 44 b and compression device 1400.Compression device 1400 contains compressor 1410.

[0075] According to the present invention, it is now possible tocompensate for delays related to turbo lag. In a preferred embodiment,during vehicle launch at low vehicle speed and low engine speed, bothinlet control device and outlet control device 170 and 171 arecoordinated to rapidly control engine cylinder charge, therebycompensating for the delayed pressure buildup from compression device1400. However, such an approach can be used throughout various drivingconditions, such as, for example, during highway cruising operation.

[0076] While the invention has been shown and described in its preferredembodiments, it will be clear to those skilled in the arts to which itpertains that many changes and modifications may be made thereto withoutdeparting from the scope of the invention. For example, as describedabove herein, any device that affects flow exiting intake manifold 44and entering cylinder 30 can be used as an outlet control device. Forexample, a swirl control valve, a charge motion control valve, an intakemanifold runner control valve, or an electronically controlled intakevalve can be used according to the present invention to rapidly changecylinder fresh charge. Further, any device that affects flow enteringintake manifold 44 can be used in place of intake control device. Forexample, an EGR valve, a purge control valve, or an intake air bypassvalve can be used in conjunction with the outlet control device sorapidly change cylinder fresh charge.

[0077] Also, the invention can be applied to any situation where enginecylinder charge needs to be controlled faster than manifold dynamicswould normally allow. Accordingly, it is intended that the invention belimited only by the following claims.

[0078] We claim:

1. A method for controlling speed of an engine having at least onecylinder, the engine also having an intake manifold and an outletcontrol device for controlling flow from the intake manifold into thecylinder, comprising: generating a desired engine speed; and changingthe outlet control device to control the engine speed to said desiredengine speed.
 2. The method recited in claim 1 wherein the enginefurther comprises an inlet control device for controlling flow into theintake manifold, wherein said changing step further comprises changingboth said inlet control device and the outlet control device in responseto a respective outlet control device command and an inlet controldevice command.
 3. The method recited in claim 2 wherein said changingstep further comprises the steps of: determining said outlet controldevice command based on a difference between said desired engine speedand the engine speed; and determining said inlet control device commandbased on said difference.
 4. The method recited in claim 2 wherein saidchanging step further comprises the steps of: determining said outletcontrol device command based on a difference between said desired enginespeed and the engine speed; and determining said inlet control devicecommand based on said outlet control device command.
 5. The methodrecited in claim 1 wherein said changing step further comprisesdetermining a desired change in the outlet control device to produce adesired engine torque.
 6. The method recited in claim 2 wherein saidinlet control device is a throttle and the outlet control device is avariable cam timing actuator.
 7. A method for controlling speed of anengine having at least one cylinder, the engine also having an intakemanifold and an outlet control device for controlling flow from theintake manifold into the cylinder and an inlet control device forcontrolling flow into the intake manifold, comprising: generating adesired engine speed; and changing both the outlet control device andthe inlet control device based on the engine speed and said desiredengine speed and in response to a respective outlet control devicecommand and an inlet control device command.
 8. The method recited inclaim 7 wherein said changing step further comprises the steps of:determining an engine speed error between said desired engine speed andthe engine speed; filtering said engine speed error; determining anintermediate inlet control device command based on said filtered enginespeed error; determining an intermediate outlet control device commandbased on a nominal desired outlet control device position and an actualoutlet control device position; determining said outlet control devicecommand based on said intermediate outlet control device command andsaid speed error; and determining said inlet control device commandbased on said intermediate inlet control device command and said enginespeed error.
 9. The method recited in claim 7 wherein said changing stepfurther comprises the steps of: determining an engine speed errorbetween said desired engine speed and the engine speed; determining adesired cylinder charge based on said engine speed error; anddetermining said inlet control device command and said outlet controldevice command based on said desired cylinder charge.
 10. The methodrecited in claim 9 wherein said inlet control device is a throttle. 11.The method recited in claim 9 wherein said outlet control device is avariable cam timing actuator.
 12. The method recited in claim 9 whereinsaid outlet control device is a swirl control valve.
 13. The methodrecited in claim 9 wherein said inlet control device is an idle airbypass valve.
 14. The method recited in claim 7 wherein said inletcontrol device and said outlet control device are changed to affect flowin similar directions to control engine speed.
 15. The method recited inclaim 14 further comprising the step of changing said inlet controldevice and said outlet control device to affect flow in oppositedirections to avoid disturbing engine torque in response to a desiredoutlet control device setpoint.
 16. The method recited in claim 14further comprising the step of changing said inlet control device andsaid outlet control device to affect flow in opposite directions toavoid disturbing engine speed in response to a desired outlet controldevice setpoint.
 17. An article of manufacture comprising: a computerstorage medium having a computer program encoded therein for controllingan engine speed, the engine having at least one cylinder, the enginealso having an intake manifold and an outlet control device forcontrolling flow from the intake manifold into the cylinder, saidcomputer storage medium comprising: code for generating a desired enginespeed; and code for adjusting the outlet control device to control theengine speed to said desired engine speed.
 18. The article recited inclaim 17 wherein the engine further comprises an inlet control devicefor controlling flow into the intake manifold, the article furthercomprising code for adjusting both the inlet control device and theoutlet control device to control the engine speed to said desired enginespeed.
 19. The article recited in claim 17 wherein said inlet controldevice is a throttle and the outlet control device is a variable camtiming system, the article further comprising: code for adjusting theinlet control device and the outlet control device to affect flow insimilar directions in response to an engine speed error; and code foradjusting the inlet control device and the outlet control device toaffect flow in opposite directions in response to an outlet controldevice setpoint error.